[llvm] [LV] Teach LoopVectorizationLegality about struct vector calls (PR #119221)

[Florian Hahn via llvm-commits]

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@@ -943,11 +955,24 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
       if (CI && !VFDatabase::getMappings(*CI).empty())
         VecCallVariantsFound = true;
 
+      auto canWidenInstruction = [this](Instruction const &Inst) {
+        Type *InstTy = Inst.getType();
+        if (isa<CallInst>(Inst) && isa<StructType>(InstTy) &&
+            canWidenCallReturnType(InstTy)) {
+          StructVecVecCallFound = true;
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fhahn wrote:

Right I see there is an already a TODO to remove the `StructVecVecCallFound`, so as long as it is temporary that's sounds OK to me. It would be good if we could make this clear with a comment here as well to avoid confusion for future readers of the code, as in most cases the checks in LVL are  directly tied to what we can generate code for.

Another alternative may worth considering is the future would be to bail out during VPlan construction if we encounter something that we cannot generate recipes for. There are a few cases where we already do that.

https://github.com/llvm/llvm-project/pull/119221